Aluminum and aluminum alloys are relatively soft materials and for many uses known in the art, it is desirable to upgrade or improve their wear and corrosion resistance. The conventional procedure for improving the wear and corrosion resistance of aluminum and its alloys is to coat the aluminum article with nickel. In order to obtain adequate adhesion of the nickel plate on the aluminum article, it is conventionally treated with an alkaline solution of sodium hydroxide containing sodium zincate and this process is usually referred to in the art as a "zincate dip". This process, however, leaves a zinc film on the aluminum article and, when plated with the nickel bath, the zinc dissolves in the nickel bath causing interference with the nickel plating and limiting the life of the nickel plating bath. In addition, the corrosion resistance (for example, salt spray) is not as good with the layer of zinc between the nickel plating and the aluminum article as it would be in the absence of the intermediate zinc layer. The high alkalinity of the zincate also tends to etch the aluminum article during the zincate dip pretreatment prior to nickel plating.
A number of attempts have been made to eliminate the shortcomings of the zincate dip, such as the use of nickel, cobalt and chromium cyanides in a solution of ammonium hydroxide as disclosed in the Satee U.S. Pat. No. 4,106,061 of April 1980. Other attempts to overcome the problems involved with the zincate process are disclosed in U.S. Pat. to Leloup, No. 3,284,323 of Nov. 8, 1966; Asada No. 3,515,650 of June 2, 1970; Bellis No. 3,672,964 of June 27, 1972; and Frasch No. 2,233,140 of Mar. 4, 1941. These patents show attempts to overcome the problems by modifying the zincate process, or, using poisonous cyanides or acid solutions to treat aluminum articles preparatory to zinc plating.